License plate registration stickers come at a high cost, especially in some states, which encourages some unethical individuals to go around stealing them instead. If you want to deter these thieves, redditor echosx suggests cutting your sticker with a razor blade:

You can deter someone from stealing the registration sticker on your license plate by cross cutting it with a razor blade. If they try to pull it off, it will only come off in pieces. This trick will still work even if you've neglected to remove the old sticker. It's recommended to remove the old sticker before placing the new one on, you can also use the razor blade to help with the removal of the old one.

Of course, the thief could always pull both pieces of the sticker but removing pieces makes it much more difficult. If you only lose a small piece, too, you may not have to worry about getting a replacement.